This is Guard Duty.
Put your feet in the shoes of Barney Calhoun, a security guard at the Black Mesa Research Facility who has no idea that the next few hours are going to change his life forever. Re-live the exciting adventure of Blue Shift, now re-created in the award winning Source engine.

"alright men, you have your squadrin's on the left door?"
"Yes sir,"
"Good, now... Inform the right squad that were about to flank in 30 seconds..."
"Yes, sir!.. SQUAD RIGHT, WE WILL BE FLANKIN' THROUGH THESE DOORS IN 30 SECONDS!."
*25 seconds later.*
"5...4...3...2...1... BREACH!"
"DO YOU SEE ANYONE?"
"NO BUT THEIR LIGHTIN' UP THE PLACE!"